High-temperature alloys



Patented Feb. 6, 1951 HIGH-TEMPERATURE ALLOYS Ray H. English, Nathaniel B. Ornitz, and Martin N. Ornitz, Pittsburgh, Pa., assignors to Blaw- Knox Company, Pittsburgh, Pa., a corporation of New Jersey No Drawing.

Application September 4, 1946,

Serial No. 694,828

1 5 Claims.

This invention provides a high temperature aly having high resistance to corrosion, low creep and high load carrying ability at elevated temperatures. Over a period of many years, there has been a demand for alloys of this character. Instrumentalities such as the gas turbine, turbo super-charger and jet propulsion motors, heat treating furnace accessories, crucibles, radiant tubes, and parts for internal combustion engines. contain parts which should resist the corrosive influence of hot products of combustion containing oxygen and/or other corrosive gases at elevated temperatures and, at the same time, retain their ability to carry high mechanical loads. The alloys heretofore available have only partially met these requirements, and in consequence, undesirable limitations on design have been imposed by th limitations of the available alloys.

Properties which are important in materials for this purpose are resistance to oxidation and stability of shape under load. As the temperatures increase, metals tend to burn more readily and also to have greater plastic deformation or creep over a period of time. Man metals which might b quite strong at high temperatures cannot be exposed to even mildly corrosive or oxidizing atmospheres at such temperatures without rapidly being consumed, while other compositions which are resistant to burning do not have rigidity.

Corrosion of alloys in hot gases is dependent, of course, on the atmosphere as well as the alloy. The behavior of metals maintained constantly under high temperature is characteristically a progressive burning away of the surface ,at asubstantially constant rate, which is measured in inches penetration per year.

The behavior of specimen metals under constant stress below the elastic limit at high temperature is characterized by three stages of deformation, namely:

1. A period of internal stress distribution tak-.

ing place in a relativel short time and characterized by an initial high and diminishing rate of deformation. This stage is made up of elastic and plastic flow.

2. A period of constant rate of deformation lasting over long periods of time. This phenomenon is known to metallurgists as creep, and is usually measured in terms of elongation per hour under a given tension, although it is equally characteristic of other deformations and we prefer to compare specimens in bending rather than in direct tension, and to express creep in terms of angular deflections per hour.

3. A final increasing rate of deformation leading to necking and failure.

The rate of deformation per unit time in stage 2 is a suitable measure of rigidity or permanence of shape of the material at the load and temperature. It is customary to select the allowable unit stress for a particular metal at a particular high temperature on the basis of the creep considered permissible at that temperature. The time to reach and pass through the diiferent stages to creep is of importance and is influenced by the material, temperature and load or unit stress.

Our alloy has high mechanical strength, low creep and also high resistance to corrosion at very high temperatures. Our alloy is equal or superior in these respects to other known alloys at lower temperatures, its relative advantages and superiority become strikingly apparent at the higher temperatures for which it is peculiarly adaptable; e. g. at temperatures such as 2300 F. It is an alloy of nickel containing as essential alloying constituents chromium, tungsten and carbon, the balance being substantially iron along with the usual contaminants in common amounts, in certain balanced proportions which we have found required to produce these unique characteristics.

The composition of alloys satisfactory at temperatures in the vicinity of 2300 F. is much more critical than the composition producing alloys for lower temperatures. High strength is attributed to insoluble precipitated phases in the alloy, which, however, are more diflicult to produce and maintain as the temperature is increased above 1800 F. Resistance to oxidation is due to the formation of a tough, adherent, protective oxide coating which is increasingly difficult to achieve as the temperature is increased, especially above 1800 F. Ingredients enhancing strength by inducing precipitation of suitable insoluble phases at 2300" F. frequently cause formation of oxides which are not effective as protective coatings, and conversely ingredients found to be effective in reducing corrosion often increase the solubility of the precipitated phases or otherwise adversely affect their strength. While alloys containing nickel, chromium, tungsten, carbon and iron are known for high temperature application, our particular composition is the first discovered to be useful for articles of the sorts previously mentioned for use at temperatures at 2 300 F.; and when the ingredi- 3 ents are combined in the proportions here set forth, the virtues of strength and resistance to oxidation are balanced to produce articles far superior to any heretofore available.

concentration. We have found, however, that molybdenum in place of tungsten in our alloy causes pitting, and furthermore, does not produce the remarkable rigidity achieved by tung- Considering for the moment only the essen- 5 sten, tial constituents the preferred analysis of the In tests at 2300 F. our alloy has been found alloy for most purposes is: to have great resistance to corrosion and ex- Per cent cellent mechanical strength. In air, the surface Ni 52 does not corrode at a rate exceeding .07 inch W 5 penetration per year, and the creep, under a "IIIILL: 27 tensile stress of 143 lbs. per square inch, is less C 050 than .00013 per cent elongation per hour. These Balance Substantially iron values are expressed in conventional units, being reduced by calculations and extrapolation from Th composition f the alloy may extend V 5 tests further described below. Because of the a fairly Wide range a1}1i St111 f f b 3 ease and accuracy with which bending tests and uniqu? (PhaTaCtenStIQS; However 15 1 can be made, we prefer to compare the creep of sirable to lim t the composition of the alloy withhigh temperature alloys in terms of rate of bend in the following range of concentrations of al g radians per hour of a horizontal bar of loymg constltuents: given section modulus loaded to a given extreme P t. fibre stress at a fixed support for one end of the 1 40- 60 bar. Expressed in these terms, the rate of bendw 4,0 6,5 ing of bars of our alloy having a section modulus Cr 22- 34 'of .0123 inF (for one half inch diameter speci- C 035-0315 25 mens) loaded to an extreme fibre stress of 143 Balance t t n iron pounds per square inch is substantially below .00010 radian per hour.

For t t to hold the1r.product to Those who require articles of rigidity even t f t hmlts the.anoy haflvmg the better than the above may achieve it with our lowmg hmlts would be satlsfactory' '30 alloy. For example, we have found it readily Per cent possible to cast bars of our alloys having a per- Ni 45- 55 cent elongation per hour when loaded to 143 W 5- 6 lbs/sq. in. tensile stress at 2300" F. not exceed- Cr 25 31 ing the extremely low value of .00005%, or cor- C 0.45-0.60 35 respondingly for beam specimens of .0123 111. Balance substantially iron section modulus, a rate of bending not exceed- The balance of the alloy, apart from its essen ing .00004 radian per hour when loaded to an tial constituents nickel, tungsten, chromium and Fextreme fibre stress of e per Square carbon, is substantially iron along with the usual mch P T combmatlon of char contaminants in common amounts. acteristics is unique with our alloy and answers Historically, the search for suitable high temlong felt f perature alloys has supported the present trend By W of fllustmtlon h lfesults 9 F and to employ cobalt in substantial amounts. This corroslon test/$011 alloys Witlnn the limits of our is a very costly ingredient and its wide use is alloy composition are given with their chemical founded not on suggestion that cobalt is a mere composltlons: V permissible substitute for nickel, but on the TABLE I now prevalent belief that unless cobalt is used in Behavior of halfmwh diameter alloy specimens substantlal amounts, a satisfactory alloy havmg under constant stress at 23000 high strength and rigidity cannot be produced.

Our alloy is superior to alloys which are characo teristically of cobalt base. While some cobalt Testlesultsamm may be used in the alloy, the properties are not enhanced thereby and an advantage of our inzfi l gleg glgl l? tililtfihflt vention resides in the economy of not requir- 9T -1 r ing this relatively expensive ingredient. Cobalt, m'gtensmn dmnspcl per in fact, has the effect of materially reducing the Alloy Au 000035 0000268 (1 06 QOIIOSlOll resistance of the alloy at temperatures Alloy B. .001035 .000027 0.08 above 2000 F. when used in amounts heretofore Alloy -000027 regarded as adequate to justify its addition to TABLE II Composition of alloy specimens in Table I Alloy Ni CO Cr W Mo Fe 0 Mn Si Cb A1 alloys successfully used at temperatures below A brief description of the manner of making 2000 F. Our alloy is preferably substantially the above tests will be necessary for a complete free from cobalt. understanding of their true worth. A test bar Molybdenum and tungsten have been heretoof each alloy is cast and machined to one-half fore considered equally valuable in promoting inch plus or minus 0.001 inch diameter, and of resistance to corrosion over the same range of suitable length for testing as a cantilever beam.

One end of the specimen is secured rigidly in a support, the bar extending horizontally therefrom, inside an enclosure through which hot products of combustion of natural gas are passed. Each bar is loaded so that the extreme fibre stress adjacent the support is precisely equal 143 lbs. per square inch in tests at 2300 F., this being a reasonable stress value at this temperature.

The temperature Within the enclosure is maintained accurately at 2300 F. as specified, within plus or minus 2, for a sufiicient time to conclude the test, which is normally run for several weeks. The deflection of the bar is measured at 48 hour intervals and reduced by calculation to angular deflection in radians. The angular deformation per hour is a direct index of the creep of the material under the specified load and temperature. The total deflection where such rates are given is very small, being less than two degrees, and the angular deformation and unit linear deformations are closely related.

Careful comparison of results of tests made in this manner withresults of direct tension tests shows that there is a direct correlation in the results. Our method of beam testing has proven to give more precise and consistent results, easily duplicated, and not subject to the variations commonly found in conventional creep tests. However, the superiority of our alloy is of great magnitude, and readily apparent from any method of testing or standard of units, in comparison with other alloys heretofore suggested.

A few words may be helpful in explanation of the corrosion results. A specimen is maintained in an atmosphere of air heated to 2300 F. for many hours, as for 500 or 1000 hours, after which it is descaled and the loss in weight determined. From this the penetration during the test period is found, and the corrosion reduced to a yearly basis by calculation. The test in air is very severe, the gases encountered ordinarily in practice being less corrosive.

While we have described and disclosed the preferred embodiment of our invention, it is to be understood that the invention is not so-limited but may be otherwise embodied and practiced within the scope of the following claims.

We claim:

1. A nickel-base alloy having new creep and corrosion-resistance properties at very high temperatures in which in air the surface does not corrode at a rate exceeding about .07 inch penetration per year and the creep is less than about .00013 per cent elongation per hour under a tensile stress of 143 pounds per square inch, consisting essentially of nickel in the range from 40% to 60%, tungsten in the range from 4% to 6.5%, chromium in the range from 22% to 34%, carbon in the range from 0.35% to 0.75%, and the balance substantially iron.

2. A nickel-base alloy having new creep and corrosion-resistance properties at very high temperatures in which in air the surface does not corrode at a rate exceeding about .07 inch penc tration per year and the creep is less than about .00013 per cent elongation per hour under a ten sile stress of 143 pounds per square inch, consisting essentially of nickel in the range from 45% to tungsten in the range from 5% to 6%, chromium in the range from 25% to 31 carbon in the range from 0.45% to 0.60%, and the balance substantially iron.

3. A nickel-base alloy having new creep and corrosion-resistance properties at very high temperatures in which in air the surface does not corrode at a rate exceeding about .07 inch penetration per year and the creep is less than about .00013 per cent elongation per hour under a tensile stress of 143 pounds per square inch,

consisting essentially of about 52% nickel, 5%

tungsten, 27% chromium, 0.5% carbon, and the balance substantially iron.

4. A nickel-base alloy having new creep and corrosion-resistance properties at very high temperatures in which in air the surface does not corrode at a rate exceeding about .07 inch penetration per year and the creep is less than about .00013 per cent elongation per hour under a tensile stress of 143 pounds per square inch, consisting essentially of nickel in the range from 40% to tungsten in the range from 4% to 6.5%, chromium in the range from 22% to 34%, carbon in the range from 0.35% to 0.75%, and. the balance substantially iron, said alloy being free from molybdenum.

5. A nickel-base alloy having new creep and corrosion-resistance properties at very high temperatures in which in air the surface does not corrode at a rate exceeding about .07 inch penetration per year and the creep is less than about .00013 per cent elongation per hour under a tensile stress or 143 pounds per square inch, consisting essentially of nickel in the range from 45% to 55%, tungsten in the range from 5% to 6%, chromium in the range from 25% to 31%, carbon in the range from 0.45% to 0.60%, and the balance substantially iron, said alloy being free from cobalt and molybdenum.

RAY H. ENGLISH. NATHANIEL B. ORNIIZ. MARTIN N. ORNITZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 20,877 Prange Oct. 4, 1938 1,504,338 Girin Aug. 12, 1924 1,572,996 Girin Feb. 16, 1926 2,381,459 Merrick Aug. 7, 1945 2,396,552 Cape Mar. 12, 1946 FOREIGN PATENTS Number Country Date 286,367 Great Britain Mar. 5, 1928 

1. A NICKEL-BASE ALLOY HAVING NEW CREEP AND CORROSION-RESISTANT PROPERTIES AT A VERY HIGH TEMPERATURES IN WHICH IN AIR THE SURFACE DOES NOT CORRODE AT A RATE EXCEEDING ABOUT .07 INCH PENETRATION PER YEAR AND THE CREEP IS LESS THAN ABOUT .00013 PER CENT ELONGATION PER HOUR UNDER A TENSILE STRESS OF 143 POUND PER SQUARE INCH, CONSISTING ESSENTIALLY OF NICKEL IN THE RANGE FROM 40% TO 60%, TUNGSTEN IN THE RANGE FROM 4% TO 6.5%, CHROMIUM IN THE RANGE FROM 22% TO 34%, CARBON IN THE RANGE FROM 0.35% TO 0.75%, AND THE BALANCE SUBSTANTIALLY IRON. 